Electro-pneumatic transducer

ABSTRACT

An electro-pneumatic transducer in which a valve member and an armature of an electro-magnetic actuator are mounted on the outboard end of a cantilever spring assembly for movement as a unit relative to a pneumatic orifice to modulate a pneumatic signal in proportion to an electrical signal applied to the stator of the electromagnetic actuator.

States Patent [1 1 Vischulis 1 Oct. 30, 1973 ELECTRO-PNEUMATIC TRANSDUCER [75] Inventor: George Vischulis, Menomonee Falls,

Wis. [73] Assignee: Rockford Servo Corporation,

Rockford, Ill.

[22] Filed: Oct. 4, 1971 [21] Appl. No.: 186,276

[52] U.S. Cl 251/129, 91/363, 137/82 [51] Int. Cl F161: 31/06 [58] Field of Search 251/129, 138;

[56] References Cited UNITED STATES PATENTS Griffith 251/129 X 3,004,546 10/1961 Robins et al 137/82 3,589,672 6/1971 Holloman 251/129 3,256,900 6/1966 Estes et a1 137/88 Primary Examiner-Arnold Rosenthal AttorneyVernon J. Pillote [57] ABSTRACT An electro-pneumatic transducer in which a valve member and an armature of an electro-magnetic actuator are mounted on the outboard end of a cantilever spring assembly for movement as a unit relative to a pneumatic orifice to modulate a pneumatic signal in proportion to an electrical signal applied to the stator of the electromagnetic actuator.

5 Claims, 2 Drawing Figures ELECTRO-PNEUMATIC TRANSDUCER BACKGROUND OF THE INVENTION In order to achieve accurate conversion of electrical to pneumatic signals in an electro-pneumatic transducer, it is necessary to minimize hysteresis, that is the difference between two curves representing the change in pneumatic signal with the applied electrical signal, when the electrical signal increases and when the electrical signal decreases. Some hysteresis in the electromagnetic transducer is due to magnetic hysteresis in the core material of the electromagnetic actuator. However, friction and lost-motion in connections between parts of the electromagnetic transducer markedly increase the overall hysteresis of the transducer.

SUMMARY OF THE INVENTION An important object of the present invention is to provide an electromagnetic transducer which minimizes the overall hysteresis of the transducer. In general, this is achieved by providing an electro-pneumatic transducer in which a valve member and the armature of an electromagnetic operator are fixedly mounted on the outboard end of a cantilever spring assembly for movement as a unit relative to a pneumatic orifice to modulate a pneumatic signal in proportion to an electrical signal applied to the stator of the electromagnetic operator which is mounted in fixed relation to the pneumatic orifice and separated from the armature by an air gap. Improved linearity of response of the transducer is effected by a cantilever spring assembly having a pair of relatively parallel spring members spaced apart in a direction paralleling the direction of movement of the valve member so as to cause the valve member and armature to maintain a preset attitude during movement with the spring assembly. The electro-pneumatic transducer is advantageously made adjustable to vary the rate of change of the pneumatic signal with the applied electrical signal and this is achieved by arranging the stator and armature of the electromagnetic operator for relative angular adjustment about an axis normal to the air gap therebetween to adjust the magnetic coupling between the stator and armature.

These, together with other objects and features of the present invention will become apparent from the following description when taken in connection with the accompanying drawings wherein:

FIG. 1 is a side elevational view of an electropneumatic transducer embodying the present invention and schematically shown applied to a web guide system; and

FIG. 2 is a top view of the eIectro-pneumatic transducer of FIG. 1.

The electro-pneumatic transducer of the present invention is generally adapted for modulating a pneumatic signal in proportion to an applied electrical signal. For purpose of illustrating application of the present invention, the transducer is diagrammatically shown in FIG. 1 applied to a web positioning system in which an electrical web positioning detector such as a photoelectric web position sensing device 11 operates through an amplifier 11a to produce an electrical output signal correlative in amplitude to the deviation of the web W from a preselected path of web travel, which output signal is applied through conductors 12 to the electro-pneumatic transducer. Air at a substantially constant low pressure is provided from a source 13 through a flow restrictor l4 and conduit 15 to the electro-pneumatic transducer, and the transducer regulates the flow of air from the conduit 15 and hence the pressure drop across restrictor 14. A pressure responsive operator 16 such as a diaphragm is connected so as to respond to the pressure in conduit 15 and operates a servo-motor, herein diagrammatically shown in the form of a hydraulic servo-valve 17 that reversibly supplies hydraulic fluid from a hydraulic fluid pressure supply source such as a pump 18 to a hydraulic positioning motor 19 connected to a movable web guide roller assembly 21.

The electro-pneumatic transducer 10 has a rigid support structure including a base 25 conveniently provided with a mounting flange 26. A pneumatic orifice is rigidly mounted on the base and, as shown, comprises an orifice member 27 threaded into the base and defining an annular valve seat 27a at its upper end. The orifice member 27 has a hose coupling 29 at its lower end and the electro-pneumatic transducer is preferably mounted closely adjacent the pressure responsive operator 16 to minimize the overall length of the conduit 15 necessary to connect the orifice with the pressure responsive operator 16.

A valve member 31 is provided for controlling the flow of air through the orifice member 227 and has a valve face 31a cooperable with the seat 27a to substantially block flow through the orifice when the valve member is in its closed position. The valve member 31 is supported for movement relative to the orifice by the cantilever spring assembly including upper and lower leaf spring members 33 and 34. One end of the leaf springs 33 and 34 are rigidly clamped to the base at a location laterally offset from the orifice and, as shown, the lower leaf spring is spaced from the base by a spacer block 35 and the upper leaf spring is spaced above the lower spring by an intermediate spacer block 36. A clamp block 36 overlies the upper spring and the blocks and leaf springs are rigidly secured to the base by a cap screw 38 that extends through openings in the blocks and leaf springs and is threaded into the base. Dowels 39 are also provided to inhibit turning of the leaf springs and blocks about the axis of the cap screw 38. The leaf springs extend in cantilever fashion from the blocks 35-37 into overlying relation with the orifice member 27 and the outboard ends of the leaf springs are maintained in parallel relation by a spacer sleeve 41 interposed between the upper and lower leaf springs and having a length equal to the height of the intermediate block 36. The valve member 31 is spaced by a sleeve 42 from the underside of the lower leaf spring 34 a distance such that the leaf spring assembly normally presses the valve face 31a on the valve member against the seat 27a. The valve member 31 is rigidly secured to the spring assembly by a screw 44 that extends through the valve member and spacer sleeve 42 and is threaded into the spacer sleeve 41.

An electro-magnetic actuator is provided for moving the valve member and includes a stator assembly 51 and an armature 52 which is separated from the stator assembly by an air gap. The stator assembly 51 is herein shown in the form of a generally E-shaped stator core formed of laminated ferromagnetic material and defining a pole face 51a at its underside. A coil 51b composed of a large number of turns is disposed around the central leg of the core and is operative,

when energized, to produce an electro-magnetic field that extends across the air gap and through the annature 52. The armature 52 is fixedly mounted on the outboard of the leaf spring assembly for movement as a unit therewith and, as shown, is spaced above the upper leaf spring 33 by a spacer sleeve 56 and is secured to the spring assembly by a cap scres 57 that extends through the armature S2, sleeve 56 and spring 33 and is threaded into the spacer sleeve 41. Thus, the armature is rigidly secured to the outboard end of the leaf spring assembly and to the valve member 31. The armature is elongated as shown in FIGS. 1 and 2 to provide an armature face 52a having the same general dimensions as the pole face 510. The fastener 57 is preferably located medially between the ends of the armature 52 so that the armature is not only attached to the valve member in an axial alignment therewith, but is also symmetrically arranged with respect to the valve member. A pin 58 is attached to the armature 52 at a location offset from the armature mounting screw 51 and loosely extends into an opening in one of the leaf springs 33 to prevent turning of the armature relative to the leaf spring assembly.

A stator assembly 51 is rigidly mounted in fixed rela tion to the orifice member by a plate 61 which is rigidly supported in spaced relation to the base 25 by tubular posts 62 and fasteners 63 that extend through the plate 61 and posts 62 and are threaded into the base. The stator assembly is rigidly mounted on the underside of the plate 61 and, for reasons set forth hereinafter, is arranged for angular adjustment with respect to the base 61 about an axis aligned with the vertical centerline of the armature. As shown, a screw 68 extends through the plate 61 and is threaded into the top of the stator core so as to allow angular adjustment of the stator assembly about an axis perpendicular to the air gap between the stator and armature and symmetrically located with respect to the pole face 51a. The screw 68 can be tightened to clamp the stator assembly in an angularly adjusted position and a locking screw 71 is threadedly mounted in the plate 61 to engage the top of the stator assembly to aid in holding it in an angularly adjusted position.

As previously described, the armature 52 is separated from the pole face 51a on the stator by an air gap and, in order to limit the minimum air gap, an adjusting screw 75, of a non-magnetic material such as brass is threadedly mounted on the stator core to project below the pole face 510 for engagement with the armature to limit the minimum air gap between the stator and armature.

A calibrating spring is also provided and is herein shown in the form of a coil-type spring 81 which engages the lower leaf spring 34 and is centered thereon as by a button 82. The coil spring extends into a bore 83 in the base and engages an adjustable abutment in the form of a screw 84 that is threaded into the bore 83 so as to apply an adjustable counter pressure to the leaf spring assembly in a direction to yieldably oppose closing movement of the valve member. With this arrangement, the valve closing pressure applied by the leaf springs 33 and 34 to the valve member 31 can be selectively adjusted. A cover 81 is advantageously provided to prevent entrance of dirt and foreign material into the transducer.

From the foregoing it is thought that the construction and operation of the electro-pneumatic transducer will be readily understood. The cantilever spring assembly including springs 33 and 34 will support the valve member 31 and armature 52 on the outboard end of the spring assembly for movement as a unit relatively to the orifice in response to the electrical signal supplied to the coil 52 on the stator assembly. The orifice member 27 defines a flow passage which is large as compared to the flow passage in restrictor 14 and the valve seat 27a and the valve member 31 define a face-type seal around the orifice so that only a very small movement of the valve member produces a wide variation and flow through the orifice. For example, with a pneumatic pressure supply source 13 supplying air at about 6 inches of water column and with a flow restrictor 14 having a cross sectional area of about 0.012 square inches, a valve movement of 0.006 to 0.008 is sufficient. The leaf spring 33 and 34 operate somewhat in the manner of parallelogram linkage to maintain the valve member in a fixed attitude with its axis generally paralleling the orifice, during movement of the valve member. The closing pressure applied to the leaf spring assembly can be selectively adjusted by the calibrating spring 81 under the control of screw 84 and the stator assembly can be angularly adjusted relative to the armature to vary the electro-magnetic coupling between the stator and armature and thereby vary the rate of response of the electro-pneumatic transducer. ln adjusting the unit, the stator is initially set at an angle relative to the armature, for example an angle of about 30, as shown in FIG. 2. An electrical signal, intermediate the levels of the maximum and minimum signals produced by the electrical signal generating apparatus ll, 12, is then applied to the coil. For example, if the electrical signal generating apparatus is capable of producing a maximum of 16 volts, an intermediate calibrating voltage of about 10 volts is applied to the coil 52 and the counter pressure applied by the calibrating spring 81 is then adjusted by screw 84 until the pressure signal sensed by the operator 16 is at an intermediate value such as 3 inches of water column and the pneumatic operator adjusting spring 16a is adjusted by adjusting screw 16b to position the servo-valve 17 in its neutral or null position at that intermediate pressure. A higher electrical signal is then applied to the coil 51b and the pressure change then noted. If the pressure change is less than desired for operating the pneumatic operator 16, the angle of the stator assembly is decreased to increase the electrical magnetic coupling. Conversely, if the pneumatic signal is greater than that desired, the angle of the stator assembly relative to the armature can be increased to decrease the electric magnetic coupling therebetween.

Since the valve member 31 and armature 52 are fixedly mounted from the outboard end of the cantilever spring assembly with the armature separated from the stator by an air gap, there is substantially no lost motion or friction in the mounting of the valve member or in the connection of the electro-magnetic armature to the valve member so that hysteresis is minimized. The dual leaf type cantilever spring assembly maintains the valve member and armature in a preset attitude during movement of the valve member and armature so as to provide a more linear response characteristic. Angular adjustment of the stator assembly relative to the armature changes the magnetic coupling and hence the rate of response of the transducer.

While a specific embodiment of the electropneumatic transducer has been herein disclosed, it will be apparent to those skilled in the art that variations and modifications in the exemplary disclosure can be made within the scope of the invention as defined in the appended claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An electro-pneumatic transducer for modulating a pneumatic signal correlative with an applied electrical signal comprising, a rigid support structure, means defining a pneumatic orifice rigid with said support structure, leaf spring means having one end fixed to said support structure at a location laterally offset from said orifice means and a free end portion extending in cantilever fashion from said one end toward said orifice means, a movable valve member fixedly mounted on said free end portion of said leaf spring means for movement therewith in a direction axially of said orifice means to control flow through said orifice means, an electro-responsive operator including a stator assembly rigidly mounted on said support structure and an electromagnetic armature rigidly mounted on said free end portion of said leaf spring means, said stator assembly having a coil operative when energized to electro-magnetically actuate said armature to move said valve member, said stator assembly having an elongated pole face disposed in a plane perpendicular to the axis of said orifice means and said armature having an elongated armature face disposed in a plane generally paralleling the plane of said pole face, one of said items comprising the armature and stator assembly being mounted for angular adjustment about an axis perpendicular to the pole face on the stator to vary the electromagnetic coupling between the stator assembly and armature.

2. An electro-pneumatic transducer according to claim 1 wherein said leaf spring means comprise a pair of generally parallel leaf springs spaced apart in a direction axially of said orifice means, means fixedly securing said valve member to the free ends of both leaf springs, said armature being non-rotatably mounted on said free ends of said leaf springs at a location axially aligned with said valve member and with said elongated armature face extending lengthwise of said leaf springs, said stator assembly being mounted on the support structure for said angular adjustment relative to said armature.

3. An electromagnetic transducer according to claim 1 including a coil type calibrating spring disposed perpendicular to said leaf spring means and having one end engaging said leaf spring means intermediate its ends, and adjustable abutment means on said support structure engaging the other end of said calibrating spring to adjust the pressure applied by the calibrating spring to said leaf spring means.

4. An electro-pneumatic transducer for modulating a pneumatic signal correlative with an applied electrical signal comprising, a rigid support structure, means defining a pneumatic orifice rigid with said support structure, leaf spring means having one end fixed to said support structure at a location laterally offset from said orifice means and a free end portion extending in cantilever fashion from said one end toward said orifice means, a movable valve member fixedly mounted on said free end portion of said leaf spring means for movement therewith in a direction axially of said orifice means to control flow through said orifice means, an electro-responsive operator including a stator assembly having a generally E-shaped stator core mounted on said support structure with the free ends of the legs of the core disposed in a plane generally perpendicular to the axis of said orifice means, an elongated electromagnetic armature mounted on said free end portion of said leaf spring means and having an elongated armature face disposed in a plane generally paralleling said plane of the free ends of the legs of the stator core, said stator assembly having a coil around the central leg of the core and operative when energized to electromagnetically actuate said armature to move said valve member, one of said items comprising the armature and stator core being mounted for angular adjustment about an axis perpendicular to said plane of the free ends of the legs of the stator core to vary the electromagnetic coupling between the armature and the stator assembly.

5. An electro-pneumatic transducer according to claim 4 wherein said armature is non-rotatably mounted on said leaf spring means with said elongated armature face extending lengthwise of the leaf spring means, and said stator assembly is mounted on the support structure for said angular adjustment relative to said armature. 

1. An electro-pneumatic transducer for modulating a pneumatic signal correlative with an applied electrical signal comprising, a rigid support structure, means defining a pneumatic orifice rigid with said support structure, leaf spring means having one end fixed to said support structure at a location laterally offset from said orifice means and a free end portion extending in cantilever fashion from said one end toward said orifice means, a movable valve member fixedly mounted on said free end portion of said leaf spring means for movement therewith in a direction axially of said orifice means to control flow through said orifice means, an electro-responsive operator including a stator assembly rigidly mounted on said support structure and an electromagnetic armature rigidly mounted on said free end portion of said leaf spring means, said stator assembly having a cOil operative when energized to electro-magnetically actuate said armature to move said valve member, said stator assembly having an elongated pole face disposed in a plane perpendicular to the axis of said orifice means and said armature having an elongated armature face disposed in a plane generally paralleling the plane of said pole face, one of said items comprising the armature and stator assembly being mounted for angular adjustment about an axis perpendicular to the pole face on the stator to vary the electromagnetic coupling between the stator assembly and armature.
 2. An electro-pneumatic transducer according to claim 1 wherein said leaf spring means comprise a pair of generally parallel leaf springs spaced apart in a direction axially of said orifice means, means fixedly securing said valve member to the free ends of both leaf springs, said armature being non-rotatably mounted on said free ends of said leaf springs at a location axially aligned with said valve member and with said elongated armature face extending lengthwise of said leaf springs, said stator assembly being mounted on the support structure for said angular adjustment relative to said armature.
 3. An electromagnetic transducer according to claim 1 including a coil type calibrating spring disposed perpendicular to said leaf spring means and having one end engaging said leaf spring means intermediate its ends, and adjustable abutment means on said support structure engaging the other end of said calibrating spring to adjust the pressure applied by the calibrating spring to said leaf spring means.
 4. An electro-pneumatic transducer for modulating a pneumatic signal correlative with an applied electrical signal comprising, a rigid support structure, means defining a pneumatic orifice rigid with said support structure, leaf spring means having one end fixed to said support structure at a location laterally offset from said orifice means and a free end portion extending in cantilever fashion from said one end toward said orifice means, a movable valve member fixedly mounted on said free end portion of said leaf spring means for movement therewith in a direction axially of said orifice means to control flow through said orifice means, an electro-responsive operator including a stator assembly having a generally E-shaped stator core mounted on said support structure with the free ends of the legs of the core disposed in a plane generally perpendicular to the axis of said orifice means, an elongated electromagnetic armature mounted on said free end portion of said leaf spring means and having an elongated armature face disposed in a plane generally paralleling said plane of the free ends of the legs of the stator core, said stator assembly having a coil around the central leg of the core and operative when energized to electromagnetically actuate said armature to move said valve member, one of said items comprising the armature and stator core being mounted for angular adjustment about an axis perpendicular to said plane of the free ends of the legs of the stator core to vary the electromagnetic coupling between the armature and the stator assembly.
 5. An electro-pneumatic transducer according to claim 4 wherein said armature is non-rotatably mounted on said leaf spring means with said elongated armature face extending lengthwise of the leaf spring means, and said stator assembly is mounted on the support structure for said angular adjustment relative to said armature. 